SPEC 4.1.2.2 • CELL DIVISION
Mitosis & The Cell Cycle
How body cells divide for growth and repair — and the precise mark-scheme language that turns a near-miss into full marks.
Only 1% Got Full Marks
Mitosis questions are some of the worst-scoring questions on Paper 1. The content is short. The mark scheme is precise. The gap between students who memorise the words and students who paraphrase is where the marks disappear.
"Only 1% of students gained full marks in this question, highlighting several misconceptions or surface levels of understanding of the events of mitosis." — AQA Higher Tier examiner report
Why This Lesson
The two most common failures: writing "genetic information" when the mark scheme requires "chromosomes", and writing "chromosomes move" when the answer demands the passive "chromosomes are pulled." In the next 10 minutes, we'll get the words exactly right.
By The End Of This Lesson
Three things you'll be able to do — every one tested directly on Paper 1.
1. Describe
Describe the three stages of the cell cycle in order, using mark-scheme phrasing.
2. State
State what mitosis produces: two genetically identical daughter cells, with the same chromosome number as the parent.
3. Distinguish
Distinguish mitosis (in eukaryotic cells like ours) from binary fission (in bacteria) — and know when each term scores.
Spec Anchor
This is spec 4.1.2.1 (chromosomes) and 4.1.2.2 (mitosis & the cell cycle). Paper 1, Higher Tier. Note: spec explicitly says you do NOT need to know the phases of mitosis (no prophase / metaphase etc.).
Chromosomes & Why Cells Divide
Before the cell cycle, two facts to lock in.
Chromosomes — Spec 4.1.2.1
The nucleus of a cell contains chromosomes, made of DNA molecules. Each chromosome carries a large number of genes. In body cells, chromosomes are normally found in pairs.
23
pairs in human body cells
46
total chromosomes
23
in each gamete (half)
Three Reasons Cells Divide
1. Growth — multicellular organisms get bigger by adding cells.
2. Replacement & repair — damaged or worn-out cells are replaced.
3. Asexual reproduction — a parent produces genetically identical offspring.
In all three cases, the daughter cells must be genetically identical to the parent. That's mitosis.
The Cell Cycle — Three Stages
The spec is precise: three stages, in this order, every time. Memorise the sequence first, then the detail.
Stage 1 — Cell growth (interphase)
Cell grows, sub-cellular structures increase, DNA replicates
Stage 2 — Mitosis
Chromosomes are pulled to opposite ends; nucleus divides
Stage 3 — Cytokinesis
Cytoplasm and cell membrane divide
2 genetically identical daughter cells
Spec Boundary
You need the three overall stages — but you do NOT need to name them. Mark schemes explicitly state "ignore names of the stages" — words like "interphase" or "cytokinesis" don't score. You also don't need the phases of mitosis (prophase, metaphase, anaphase, telophase). Describe what happens; don't name it.
Stage 1 — Cell Growth & DNA Replication
Before a cell can divide, it has to prepare. Three things happen, all at once.
What Happens
The cell grows in size.
The number of sub-cellular structures increases — specifically mitochondria and ribosomes.
The DNA replicates — each chromosome is copied to form two identical copies.
Mark-scheme phrase
"DNA / chromosomes replicate / duplicate" · "mitochondria / ribosomes increase in number"
Words That Don't Score
Mark schemes ignore: "DNA divides" (wrong process — DNA replicates, doesn't divide) · "genetic material doubles" (too vague — name chromosomes or DNA) · "cell grows" alone (must be qualified with sub-cellular structures).
Stage 2 — Mitosis
The cell is now ready. The chromosomes are doubled. Now they need to be separated into two sets.
What Happens
One set of chromosomes is pulled to each end of the cell (the two "poles").
The nucleus divides.
Mark-scheme phrase
"One set of chromosomes is pulled / moved to each end of the cell."
Passive Voice — Mark-Scheme Strict
Chromosomes do NOT move themselves. Spindle fibres pull them. Examiner reports flag students who write "the chromosomes move to each end" or "the chromosomes are unable to move" — both lose the mark. The correct phrasing is passive: "are pulled" or "are moved."
Memory Tip
Think of the chromosomes as luggage on an airport conveyor belt — they don't walk themselves; they're carried. Same idea: chromosomes are pulled by the cell's machinery.
Stage 3 — Cytokinesis
The chromosomes are separated. The nucleus has divided. Now the rest of the cell physically splits.
What Happens
The cytoplasm divides.
New cell membranes form between the two halves.
Result: two new cells, each with a full set of chromosomes.
Mark-scheme phrase
"The cytoplasm and cell membrane divide (to form two cells)." Some mark schemes also accept "cytoplasm divides and new cell membranes form."
Stages Are Strictly Sequential
The cell cycle has a strict order: grow + DNA replicate → chromosomes pulled apart → cytoplasm and membrane divide. Many questions explicitly ask you to describe the stages "in order" — getting the sequence right ensures every marking point lands cleanly. Always: prepare → separate → split.
What Mitosis Produces
Three facts about the daughter cells. Mark schemes test all three.
FeatureDaughter cells from mitosis
NumberTwo daughter cells
Genetic contentGenetically identical — to each other AND to the parent cell
Chromosome numberSame number as the parent (e.g. 46 in human body cells)
Don't Confuse With Meiosis
Meiosis (covered in Module 6) produces FOUR gametes that are genetically DIFFERENT, with HALF the chromosome number. The most common error on Paper 1 mitosis questions is borrowing meiosis numbers. Mitosis = 2, identical, same number.
Why "Identical" Matters
If new skin cells weren't genetically identical to the cells they replace, they wouldn't function. Mitosis is the body's copy-paste mechanism. Meiosis is the shuffle mechanism — different jobs.
Worked Example — Cell Cycle Description
The most common cell-cycle question. Four marks. Each marking point matches one stage of the cycle.
Describe what happens in a body cell during one complete cell cycle to produce two new cells.4 marks
📋 Pattern: Chronological description — one MP per stage, in order
Strategy
Match your answer to the stages: Stage 1 (grow + DNA replicate), Stage 2a (chromosomes pulled), Stage 2b/3 (cytoplasm divides). Four marks, four stages. Don't waste sentences on phrasing that won't score.
Worked Example — Four Steps
One step per marking point. Use the mark-scheme verbs (replicate, pulled, divide).
Step 1 — Cell prepares
"The cell grows in size and the number of sub-cellular structures (such as mitochondria and ribosomes) increases."
Step 2 — DNA copied
"The DNA in the nucleus then replicates, so each chromosome forms two identical copies."
Step 3 — Chromosomes separated (mitosis)
"During mitosis, one set of chromosomes is pulled to each end of the cell, and the nucleus divides."
Step 4 — Cell splits (cytokinesis)
"Finally, the cytoplasm and cell membrane divide to form two genetically identical daughter cells."
Worked Example — Mark Scheme Tick-Off
Four marking points. Each line of your answer maps to one tick.
✓
MP1: Sub-cellular structures (mitochondria / ribosomes) increase in number
✓
MP2: DNA / chromosomes replicate (or duplicate / are copied)
✓
MP3: One set of chromosomes is pulled / moved to each end of the cell
✓
MP4: Cytoplasm and cell membrane divide (to form two cells)
Mark-Scheme Ignores
Mark schemes typically ignore: names of stages (interphase, prophase, etc.), the phrase "genetic material" alone, "DNA doubles / reproduces", "cell grows" alone (unqualified), "nucleus divides" alone (you need cytoplasm + membrane). Use the verbs that score.
The Big Lesson
Examiner reports flag this question type as one of the worst-scoring on Paper 1 because students paraphrase. Mark schemes reward specific words — replicate, pulled, cytoplasm and membrane divide. Memorise the verbs.
Mitosis In Living Organisms
The spec asks you to "recognise and describe situations where mitosis is occurring." Four examples to know.
Growing embryo
From a single fertilised egg, the embryo grows by repeated mitotic division. By birth, a human has trillions of cells — all from mitosis.
Tissue repair
When you cut yourself, new skin cells form by mitosis to replace the damaged ones. Every wound that heals is mitosis at work.
Plant growth
Meristem tissue in root tips and shoot tips contains undifferentiated cells that divide by mitosis. This is how plants grow taller and longer.
Asexual reproduction
Some single-celled eukaryotes (e.g. amoeba) reproduce by mitotic division — producing genetically identical offspring from a single parent.
Bacteria Are NOT Mitosis
Bacteria divide by binary fission, not mitosis. Bacteria are prokaryotes — they have no nucleus, so mitosis (which needs a nucleus to divide) cannot apply. Mark schemes for bacteria questions explicitly state "do not accept mitosis."
Practice Question
A liver cell undergoes mitosis.
Describe the number and genetic content of the daughter cells produced.2 marks
MP1
Number: Mitosis produces two daughter cells.
MP2
Genetic content: The daughter cells are genetically identical — to each other and to the parent cell.
⚠️
Lose-the-mark traps: writing "four cells" (that's meiosis); writing "similar" or "almost identical" (mark schemes require identical); writing "genetic information" instead of being explicit about identical DNA / chromosomes.
Three Examiner Alerts
The three traps that cost the most marks on mitosis questions across recent Higher Tier papers.
Alert 1 — Use "Chromosomes"
Mark schemes require the word "chromosomes". Phrases like "genetic information" or "genetic material" are typically marked as ignore — they don't score the point. If the answer involves something being copied, separated, or pulled, name chromosomes (or specifically DNA) explicitly.
Alert 2 — Chromosomes Are PULLED
Examiner reports flag this repeatedly: students write "chromosomes move" or "chromosomes are unable to move". Both lose the mark. Chromosomes do not move themselves — spindle fibres pull them. Use the passive: "chromosomes are pulled to each end of the cell."
Alert 3 — Bacteria = Binary Fission
Bacteria divide by binary fission, NOT mitosis. Mark schemes for bacterial reproduction questions explicitly state "do not accept mitosis." Why? Bacteria have no nucleus to divide. Same word ban applies in reverse — don't write "binary fission" for human or plant cells.
Common Errors That Cost Marks
Four wrong-vs-right pairs lifted directly from mark-scheme guidance.
✗ Wrong
"DNA divides"Wrong process. DNA doesn't divide — it replicates first.
✓ Right
"DNA replicates / chromosomes are copied"Then chromosomes are pulled apart in mitosis.
✗ Wrong
"Mitosis makes 4 daughter cells"That's meiosis. Common confusion.
✓ Right
"Mitosis makes 2 genetically identical daughter cells"Two — identical — same chromosome number.
✗ Wrong
"Chromosomes move to each end"Active voice. Loses the mark.
✓ Right
"Chromosomes are pulled to each end"Passive voice — they're moved by spindle fibres.
✗ Wrong
"Bacteria divide by mitosis"Mark schemes: "do not accept mitosis."
✓ Right
"Bacteria divide by binary fission"Prokaryotes have no nucleus — different process.
Three Things To Remember
The whole lesson, distilled to three takeaways.
1. Cell Cycle Order
Stage 1: cell grows + sub-cellular structures increase + DNA replicates.
Stage 2: chromosomes are pulled to each end; nucleus divides (mitosis).
Stage 3: cytoplasm and cell membrane divide (cytokinesis).
2. The Products
Mitosis produces two daughter cells, genetically identical to the parent and to each other, with the same chromosome number as the parent (e.g. 46 in humans).
3. The Word Bank
Use chromosomes (not "genetic material"). Use are pulled (not "move"). Use binary fission for bacteria (not "mitosis"). Mark schemes are strict on these words.
Final Word
Cell cycle questions are content-light but language-heavy. There's almost nothing to memorise — but you have to memorise the exact verbs. Get the verbs right and full marks are routine.
Next: Lesson 1.05 — Stem Cells
What stem cells are, where they come from, and how they're used in medicine and farming. Plus the ethical questions you may be asked to evaluate.
Coming Up
The mark-scheme definitions of stem cell , embryonic stem cell , adult stem cell , and meristem .
What therapeutic cloning is and how it could treat disease.
How to write a balanced evaluation of stem cell use — the question pattern that scores 4–6 marks.
Before You Move On
Practise writing the cell cycle out from memory — three stages, in order, with the mark-scheme verbs. Then take the end-of-lesson test. The verbs only stick if you write them.
Next: Only 1% Got Full Marks